The aim of this proposal is to continue our study by genetic means of several well-defined systems in which proteins and lipids interact. Such interactions are essential to the assembly and function of biological membranes. The systems are i) the bacterial enzyme cyclopropane fatty acid synthase, ii) morphogenesis of the lipid-containing bacteriophage PR4, and iii) malate oxidase, an enzyme which is activated by phospholipids. Cyclopropane fatty acid synthase is the only discrete enzyme known to specifically react with the nonpolar portion of a phospholipid bilayer. We propose to prepare large quantities of this enzyme by recombinant DNA techniques and to study its detailed interaction with its phospholipid substrate. Phage PR4 acquires its capsid lipid from the bacterial membrane and this process is a good model to study membrane morphogenesis by genetic means. We propose to use a combination of genetics and biochemistry to study the mechanisms whereby the phage lipids are acquired. Malate oxidase, a new project, is an enzyme that is greatly activated by phospholipids. We wish to isolate mutants of this enzyme defective in activation by lipids to determine the role of lipid binding in malate oxidase function.